Gathering up a few things from the comments:
A prescription is the full set of instructions issued by a doctor or other medical professional that is given to the pharmacist (or sent to them electronically) that authorizes the distribution of the medicine. A prescription can also mean the full amount of the medicine issued as a result of the doctor's prescription.
One thing the prescription will specify is the dosage regimen, which is defined at the link I've given here as:
The schedule of doses of a therapeutic agent per unit of time, including: the time between doses (e.g., every 6 hours) or the time when the dose(s) are to be given (e.g., at 8 a.m. and 4 p.m. daily), and the amount of a medicine (e.g., number of capsules) to be given at each specific time.
You can use the modifier dosage to specify any part of that regimen:
- Dosage frequency is how often the medicine is administered, like "three times per day."
- Dosage time is time(s) when it's administered.
- Dosage timing could be instructions like "before each meal" that are less precise than specific times.
- Dosage amount (or just dose) is the quantity administered at one time.
- Dosage form is the physical form of the medicine (pill, capsule, injection, etc.).
In the context of a spreadsheet, you might be able to leave off the repeated "dosage", especially if you can put "dosage regimen" in a heading over all parts of the regimen.